Crohn's disease and ulcerative colitis constitute the major forms of chronic inflammatory bowel diseases. These disorders occur in young adults with an estimated prevalence of more than 1/1000 inhabitants in western countries. Last year, our group reported a significant linkage of Crohn's disease to pericontromeric chromosome 16. This finding has since been replicated by four independent groups. A new European collaborative group has just been established to continue and expand the collection of Crohn's disease families from several European countries. These new families will assist current efforts to perform fine mapping of the chromosome 16 region and ultimately to isolate this gene. This large collection of families will also be used in further efforts to locate genes conferring susceptibility to Crohn's disease.